1. Field of the Invention
The present invention relates to etching and cleaning methods and etching and cleaning apparatuses used for semiconductor device fabrication and more particularly, to etching and cleaning methods of removing an unnecessary or undesired material or materials from a semiconductor wafer and etching and cleaning apparatuses used for performing the etching or cleaning method.
2. Description of the Prior Art
In the processes of fabricating semiconductor devices on a semiconductor wafer, various etching methods are usually used to remove unnecessary or undesired materials from the wafer and various cleaning methods are usually used to clean contaminants attached to the wafer or devices. In these cases, there is the need to remove unnecessary or undesired materials existing on the surface peripheral area of the wafer, on the back peripheral area of the wafer, or on the end face of the wafer.
Here, the xe2x80x9cend facexe2x80x9d means the end face of the wafer located between its surface and back and approximately perpendicular to them. The xe2x80x9csurface peripheral areaxe2x80x9d means the area or region of the surface of the wafer between the device area and the end face. The device area is an area or region of the surface of the wafer in which desired semiconductor devices are formed. The xe2x80x9cback peripheral areaxe2x80x9d means the area or region of the back of the wafer in which an undesired or unnecessary material or materials to be removed are present.
In recent years, copper (Cu) has been used as a wiring or interconnection material instead of aluminum (Al), because Cu is higher in conductivity than Al. In this case, Cu wiring lines are typically formed in trenches of a silicon dioxide (SiO2) film, which are usually realized by the step of forming the trenches in the SiO2 film, the step of forming a Cu film on the SiO2 film to cover the trenches by electroplating, and the step of selectively removing the Cu film to leave the same in the trenches by Chemical Mechanical Polishing (CMP). This method is termed the xe2x80x9cdamascene processxe2x80x9d.
Next, the damascene process for the Cu wiring lines is explained in detail.
First, trenches are formed in a SiO2 film to have a pattern for desired wiring lines by a known method, where the SiO2 film is formed on or over a single-crystal silicon (Si) wafer or substrate. Second, a barrier metal film, which is made of meal such as tantalum (Ta) and tantalum nitride (TaN), is formed on the SiO2 film to cover the trenches by sputtering. The barrier metal film is to prevent the Cu atoms from diffusing into the SiO2 film. Third, a seed Cu film is formed on the barrier metal film by sputtering. Fourth, a wiring Cu film is formed on the seed Cu film by electroplating.
In the fourth step of forming the wiring Cu film by electroplating, a ring-shaped blocking member is placed on the surface of the wafer to surround the device area and then, a proper plating liquid or solution is supplied to the inside of the member. At this time, there is a possibility that the plating liquid leaks out of the member. If leakage of the liquid occurs, the wiring Cu film is formed not only in the device area but also in the surface peripheral area of the wafer. The wiring Cu film thus formed in the surface peripheral area is unnecessary and to be removed. The unnecessary Cu film tends to be detached from the SiO2 film in the subsequent process or processes due to stress to thereby contaminate the production lines of the semiconductor device, because of weak adhesion of the plated Cu film to the SiO2 film. As a result, the unnecessary Cu film needs to be removed.
Moreover, after the CMP process is completed, the Si wafer is contaminated by Cu wastes produced from the Cu film polished. The Cu wastes tend to diffuse into the SiO2 film and the Si wafer due to subsequent heat treatment, thereby badly affecting the performance of the semiconductor devices formed in the device area. Since the Cu wastes adhere onto the surface and back peripheral areas and the end face of the wafer, they are difficult to be removed therefrom. Thus, the Cu wastes need to be removed by cleaning.
When the Si wafer is 8 inches in diameter, the distance between the edge of the device area and the end face of the wafer is typically set as, for example, approximately 5 mm. To expand the device area, it is preferred that the SiO2 film (in which the Cu wiring lines are formed) is formed on the wafer to be expanded until the distance between the edge of the SiO2 film and the end face is decreased to 1.5 mm to 2.0 mm. In this case, however, when the seed Cu film is deposited onto the barrier metal film over the whole wafer by sputtering in order to cover the whole SiO2 film, it tends to cover not only the device area but also the surface and back peripheral areas and the end face of the wafer. Thus, if the plating liquid or solution supplied to the inside of the ring-shaped blocking member leaks out, the wiring Cu film tends to be formed on the seed film not only in the device area but also in the surface and back peripheral areas and the end face.
Since the wiring Cu film is formed on the seed Cu film, it is not separated or stripped off. However, the wiring Cu film existing on the end face of the wafer tends to be adhered onto the wafer carriers and/or the robot arms during transportation processes in the semiconductor device fabrication system. Thus, it tends to contaminate the transportation subsystem. This means that the wiring Cu film existing on the surface and back peripheral areas and the end face of the wafer needs to be removed before the wafer is transported to the next stage.
Furthermore, the removal of the above-described wiring Cu film requires good controllability. This is because the distance between the edge of the SiO2 film and the end face is as short as 1.5 mm to 2 mm. The cleaning of the above-described Cu contaminants generated in the CMP process also necessitates similar good controllability.
To remove the undesired or unnecessary Cu film or contaminants explained above, various etching and cleaning methods have been developed and disclosed, two examples of which are shown in FIGS. 1 and 2.
In the prior-art cleaning/etching method as shown in FIG. 1, a protection film 112 having an etch-resistant property is selectively formed on the surface 110A of a semiconductor wafer 110 to cover the entire device area formed thereon. Then, the wafer 110 with the film 112 is entirely immersed into an etching solution 114 stored in a suitable container 113, thereby etching selectively the exposed area of the wafer 110. Thus, the exposed area is cleaned. Thereafter, the film 112 is removed from the wafer 110.
As the etching solution 114, for example, a mixture of hydrogen fluoride (HF), hydrogen peroxide (H2O2), and water (H2O), which is often termed xe2x80x9cFluoric-Peroxide Mixture (FPM)xe2x80x9d, may be used.
In the prior-art cleaning/etching method as shown in FIG. 2, a semiconductor wafer 110 is rotated in a horizontal plane by a proper rotating means while it is turned upside down. In this state, an etching solution 114 (e.g., FPM) is supplied downward toward the center of the back 110B of the wafer 110. At the same time as this, a protection gas 115 (e.g., nitrogen gas, N2) is supplied upward toward the center of the surface 110A of the wafer 110.
The solution 114 thus supplied onto the back 110B moves outward to the end face 110C of the wafer 110 along the back 110B and then, flows along the vertical end face 110C, and drops from the end face 110C. Part of the solution 114 reaches the periphery of the surface 110A and then, it is dropped therefrom.
The protection gas 115 thus supplied to the surface 110A keeps the device area not to be contacted with the etching solution 114. The solution 114 selectively etches the back 110B, the end face 110C, and the periphery of the surface 110A, thereby cleaning them.
With the prior-art cleaning/etching method as shown in FIG. 1, there is a disadvantage that some contrivance is required for the protection film 112 not to be formed in the periphery of the surface 110A of the wafer 110. Also, it is essential that the semiconductor devices and wiring lines formed in the device area are not damaged by removal of the protection film 112 form the surface 110A. However, this is difficult to be realized. If the protection film 112 is made of a resist material, the number of the necessary process steps is increased.
With the prior-art cleaning/etching method as shown in FIG. 2, the flow of the etching solution 114 toward the back 110B of the wafer 110 is controlled by the rotation speed of the wafer 110 and the flow rate of the protection gas 115 toward the surface 110A. Thus, the controllability is low.
Furthermore, the circular edge of the flowing solution 114, which is defined by contact or collision of the solution 114 with the gas 115 and extends along the edge of the wafer 110, tends to wave or fluctuate. As a result, the solution 114 may reach the device area at some location to etch the same. Alternately, the solution 114 does not contact with the periphery of the surface 110A at some location, leaving the undesired material thereon.
As a result, the prior-art cleaning/etching method shown in FIG. 2 is unable to be applied to the case where the distance between the edge of the device area and the end face of the wafer is as short as 1.5 mm to 2.0 mm.
Accordingly, an object of the present invention is to provide an etching method and an etching apparatus that make it possible to effectively remove an unnecessary material or materials existing on a semiconductor wafer without damaging the device area.
Another object of the present invention is to provide an etching method and an etching apparatus that make it possible to effectively remove an unnecessary material or materials existing on a semiconductor wafer with good controllability.
Still another object of the present invention is to provide an etching method and an etching apparatus that removes effectively an unnecessary material or materials existing on a semiconductor wafer even if the distance between the edge of the device area and the end face of the wafer is as short as approximately 1.5 mm to 2.0 mm.
A further object of the present invention is to provide a cleaning method and a cleaning apparatus that make it possible to effectively clean a semiconductor wafer without damaging the device area.
A still further object of the present invention is to provide a cleaning method and a cleaning apparatus that make it possible to effectively clean a semiconductor wafer with good controllability.
A still further object of the present invention is to provide a cleaning method and a cleaning apparatus that cleans effectively a semiconductor wafer even if the distance between the edge of the device area and the end face of the wafer is as short as approximately 1.5 mm to 2.0 mm.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, an etching apparatus is provided, which is comprised of:
(a) a rotating means for holding a semiconductor wafer and for rotating the wafer in a horizontal plane;
the wafer having a device area and a surface peripheral area on its surface;
the surface peripheral area being located outside the device area; and
(b) an edge nozzle for emitting an etching liquid toward a surface peripheral area of the wafer.
The etching liquid emitted from the edge nozzle selectively etches out an unnecessary material existing in the surface peripheral area of the wafer.
With the etching apparatus according to the first aspect of the present invention, the edge nozzle emits the etching liquid toward the surface peripheral area of the wafer while rotating the wafer in a horizontal plane. Thus, the etching liquid emitted to the surface peripheral area does not move inward due to a centrifugal force generated by rotation of the wafer. As a result, the unnecessary material existing in the surface peripheral area of the wafer is effectively removed without damaging the device area of the wafer.
Moreover, the emission of the etching liquid is controlled by the rotation speed of the wafer and the flow rate of the liquid and therefore, the etching action can be carried out with good controllability. This means that even if the distance between the edge of the device area and the end face of the wafer is as short as approximately 1.5 mm to 2.0 mm, the unnecessary material existing on the wafer can be removed effectively.
In a preferred embodiment of the etching apparatus according to the first aspect of the invention, the etching liquid emitted from the edge nozzle has an emission direction oriented along a rotation direction of the wafer or outward with respect to a tangent of the wafer formed near a contact point of the liquid with the surface peripheral area of the wafer.
In another preferred embodiment of the etching apparatus according to the first aspect of the invention, a back nozzle is additionally provided. The back nozzle emits an etching liquid toward a back center of the wafer. The etching liquid emitted from the back nozzle etches out an unnecessary material existing on a back of the wafer. In this embodiment, there is an additional advantage that not only the unnecessary material existing in the surface peripheral area of the wafer but also that existing on the back of the wafer can be removed simultaneously.
In still another preferred embodiment of the etching apparatus according to the first aspect of the invention, a surface nozzle is additionally provided. The surface nozzle emits a protecting liquid toward a surface center of the wafer. The protecting liquid emitted from the surface nozzle covers the device area of the wafer to protect the same against the etching liquid emitted from the edge nozzle. In this embodiment, there is an additional advantage that the device area can be prevented from being damaged due to the etching liquid emitted from the edge nozzle even if part of the etching liquid is jumped into the device area from the surface peripheral area.
In a further preferred embodiment of the etching apparatus according to the first aspect of the invention, a back nozzle and a surface nozzle are additionally provided. The back nozzle emits an etching liquid toward a back center of the wafer. The etching liquid emitted from the back nozzle etches out an unnecessary material existing on a back of the wafer. The surface nozzle emits a protecting liquid toward a surface center of the wafer. The protecting liquid emitted from the surface nozzle covers the device area of the wafer to protect the same against the etching liquid emitted from the edge nozzle.
In a still further preferred embodiment of the etching apparatus according to the first aspect of the invention, the etching liquid emitted from the edge nozzle is beam-shaped. In this embodiment, there is an additional advantage that the controllability is further improved.
The rotating means may be in any form if it can hold the semiconductor wafer and rotate it in a horizontal plane. However, it is preferred that the rotating means may be in any one of the following forms.
The rotating means may be of a roller-chucking type, in which the means comprises rollers arranged along an end face of the wafer. The rollers are contacted with the end face of the wafer to hold the wafer and rotated synchronously.
The rotating means may be of a pin-chucking type, in which the means comprises pins supported by a supporting member and arranged along an end face of the wafer. The pins are contacted with the end face of the wafer to hold the wafer and rotated synchronously by the member.
The rotating means may be of a pin-chucking type, in which the means comprises a first plurality of pins and a second plurality of pins supported by a supporting member. The first plurality of pins and the second plurality of pins are alternately arranged along an end face of the wafer. The first plurality of pins and the second plurality of pins are alternately contacted with the end face of the wafer to hold the wafer and rotated synchronously by the member.
The rotating means may be of a pin-chucking type, in which the means comprises a first plurality of pins and a second plurality of pins supported by a supporting member. The first plurality of pins are arranged along an end face of the wafer. The second plurality of pins are arranged along the end face of the wafer. The first plurality of pins are contacted with the end face of the wafer to hold the wafer and rotated synchronously by the member in a period. The second plurality of pins are contacted with the end face of the wafer to hold the wafer and rotated synchronously by the member in another period.
According to a second aspect of the present invention, a cleaning apparatus is provided, which is comprised of:
(a) a rotating means for holding a semiconductor wafer and for rotating the wafer in a horizontal plane;
the wafer having a device area and a surface peripheral area on its surface;
the surface peripheral area being located outside the device area; and
(b) an edge nozzle for emitting a cleaning liquid toward a surface peripheral area of the wafer.
The cleaning liquid emitted from the edge nozzle selectively removes an unnecessary material existing in the surface peripheral area of the wafer.
With the cleaning apparatus according to the second aspect of the present invention, the edge nozzle emits the cleaning liquid toward the surface peripheral area of the wafer while rotating the wafer in a horizontal plane. Thus, the cleaning liquid emitted to the surface peripheral area does not move inward due to a centrifugal force generated by rotation of the wafer. As a result, the unnecessary material existing in the surface peripheral area of the wafer is effectively removed without damaging the device area of the wafer.
Moreover, the emission of the cleaning liquid is controlled by the rotation speed of the wafer and the flow rate of the liquid and therefore, the cleaning action can be carried out with good controllability. This means that even if the distance between the edge of the device area and the end face of the wafer is as short as approximately 1.5 mm to 2.0 mm, the unnecessary material or materials existing on the wafer can be removed effectively.
In a preferred embodiment of the cleaning apparatus according to the second aspect of the invention, the cleaning liquid emitted from the edge nozzle has an emission direction oriented along a rotation direction of the wafer or outward with respect to a tangent of the wafer formed near a contact point of the liquid with the surface peripheral area of the wafer.
In another preferred embodiment of the etching apparatus according to the second aspect of the invention, a back nozzle is additionally provided. The back nozzle emits a cleaning liquid toward a back center of the wafer. The cleaning liquid emitted from the back nozzle removes an unnecessary material existing on a back of the wafer. In this embodiment, there is an additional advantage that not only the unnecessary material existing in the surface peripheral area of the wafer but also that existing on the back of the wafer can be removed simultaneously.
In still another preferred embodiment of the cleaning apparatus according to the second aspect of the invention, a surface nozzle is additionally provided. The surface nozzle emits a protecting liquid toward a surface center of the wafer. The protecting liquid emitted from the surface nozzle covers the device area of the wafer to protect the same against the cleaning liquid emitted from the edge nozzle. In this embodiment, there is an additional advantage that the device area can be prevented from being damaged due to the cleaning liquid emitted from the edge nozzle even if part of the cleaning liquid is jumped into the device area from the surface peripheral area.
In a further preferred embodiment of the cleaning apparatus according to the second aspect of the invention, a back nozzle and a surface nozzle are additionally provided. The back nozzle emits a cleaning liquid toward a back center of the wafer. The cleaning liquid emitted from the back nozzle removes an unnecessary material existing on a back of the wafer. The surface nozzle emits a protecting liquid toward a surface center of the wafer. The protecting liquid emitted from the surface nozzle covers the device area of the wafer to protect the same against the cleaning liquid emitted from the edge nozzle.
In a still further preferred embodiment of the cleaning apparatus according to the second aspect of the invention, the cleaning liquid emitted from the edge nozzle is beam-shaped. In this embodiment, there is an additional advantage that the controllability is further improved.
In the cleaning apparatus according to the second aspect of the invention also, the rotating means may be in any form if it can hold the semiconductor wafer and rotate it in a horizontal plane. However, it is preferred that the rotating means may be in any one of the following forms as described about the etching apparatus according to the first aspect.
According to a third aspect of the present invention, an etching method is provided, which is comprised of the steps of:
(a) rotating a semiconductor wafer in a horizontal plane;
the wafer having a device area and a surface peripheral area on its surface;
the surface peripheral area being located outside the device area; and
(b) emitting an etching liquid toward a surface peripheral area of the wafer by an edge nozzle, thereby selectively etching out an unnecessary material existing in the surface peripheral area.
With the etching method according to the third aspect of the present invention, because of the same reason as described about the etching apparatus according to the first aspect, the unnecessary material existing in the surface peripheral area of the wafer is effectively removed without damaging the device area of the wafer. Also, the etching action can be carried out with good controllability. Thus, even if the distance between the edge of the device area and the end face of the wafer is as short as approximately 1.5 mm to 2.0 mm, the unnecessary material existing on the wafer can be removed effectively.
In a preferred embodiment of the etching method according to the third aspect of the invention, the etching liquid emitted from the edge nozzle has an emission direction oriented along a rotation direction of the wafer or outward with respect to a tangent of the wafer formed near a contact point of the liquid with the surface peripheral area of the wafer.
In another preferred embodiment of the etching method according to the third aspect of the invention, an etching liquid is emitted toward a back center of the wafer by a back nozzle, thereby etching out an unnecessary material existing on a back of the wafer. In this embodiment, there is an additional advantage that not only the unnecessary material existing in the surface peripheral area of the wafer but also that existing on the back of the wafer can be removed simultaneously.
In still another preferred embodiment of the etching method according to the third aspect of the invention, a protecting liquid is emitted toward a surface center of the wafer by a surface nozzle, thereby covering the device area of the wafer to protect the same against the etching liquid emitted from the edge nozzle. In this embodiment, there is an additional advantage that the device area can be prevented from being damaged due to the etching liquid emitted from the edge nozzle even if part of the etching liquid is jumped into the device area from the surface peripheral area.
In a further preferred embodiment of the etching method according to the third aspect of the invention, an etching liquid is emitted toward a back center of the wafer by a back nozzle, thereby etching out an unnecessary material existing on a back of the wafer, and a protecting liquid is emitted toward a surface center of the wafer by a surface nozzle, thereby covering the device area of the wafer to protect the same against the etching liquid emitted from the edge nozzle.
In a still further preferred embodiment of the etching method according to the third aspect of the invention, the etching liquid emitted from the edge nozzle is beam-shaped. In this embodiment, there is an additional advantage that the controllability is further improved.
According to a fourth aspect of the present invention, a cleaning method is provided, which is comprised of the steps of:
(a) rotating a semiconductor wafer in a horizontal plane;
the wafer having a device area and a surface peripheral area on its surface;
the surface peripheral area being located outside the device area; and
(b) emitting a cleaning liquid toward a surface peripheral area of the wafer by an edge nozzle, thereby selectively removing an unnecessary material existing in the surface peripheral area.
With the cleaning method according to the fourth aspect of the present invention, because of the same reason as described about the cleaning apparatus according to the second aspect, the unnecessary material existing in the surface peripheral area of the wafer is effectively removed without damaging the device area of the wafer. Also, the cleaning action can be carried out with good controllability. Thus, even if the distance between the edge of the device area and the end face of the wafer is as short as approximately 1.5 mm to 2.0 mm, the unnecessary material existing on the wafer can be removed effectively.
In a preferred embodiment of the cleaning method according to the fourth aspect of the invention, the cleaning liquid emitted from the edge nozzle has an emission direction oriented along a rotation direction of the wafer or outward with respect to a tangent of the wafer formed near a contact point of the liquid with the surface peripheral area of the wafer.
In another preferred embodiment of the cleaning method according to the fourth aspect of the invention, a cleaning liquid is emitted toward a back center of the wafer by a back nozzle, thereby etching out an unnecessary material existing on a back of the wafer. In this embodiment, there is an additional advantage that not only the unnecessary material existing in the surface peripheral area of the wafer but also that existing on the back of the wafer can be removed simultaneously.
In still another preferred embodiment of the cleaning method according to the fourth aspect of the invention, a protecting liquid is emitted toward a surface center of the wafer by a surface nozzle, thereby covering the device area of the wafer to protect the same against the cleaning liquid emitted from the edge nozzle. In this embodiment, there is an additional advantage that the device area can be prevented from being damaged due to the cleaning liquid emitted from the edge nozzle even if part of the cleaning liquid is jumped into the device area from the surface peripheral area.
In a further preferred embodiment of the cleaning method according to the fourth aspect of the invention, a cleaning liquid is emitted toward a back center of the wafer by a back nozzle, thereby removing an unnecessary material existing on a back of the wafer, and a protecting liquid is emitted toward a surface center of the wafer by a surface nozzle, thereby covering the device area of the wafer to protect the same against the cleaning liquid emitted from the edge nozzle.
In a still further preferred embodiment of the cleaning method according to the fourth aspect of the invention, the cleaning liquid emitted from the edge nozzle is beam-shaped. In this embodiment, there is an additional advantage that the controllability is further improved.